A so-called graft for reinforcing or replacing a wall in a hollow cavity in the body, such as an artery, vein or the like can to advantage have the form of a helix spring which, when it is released at the place of implantation, expands its radial configuration with relative turning of its ends about its axis. For enabling the insertion of the element into the intended location with the aid of the device, the latter is conventionally formed in the mannner explained above. The spring element is wound up on the mandrel, which has a diameter less than the diameter of the unbiased spring element, the ends of the latter being releasably connected to the axially separated element fasteners on the mandrel. These fasteners are mutually relatively rotatable about the mandrel axis. When the spring element is wound on to the mandrel, it strives to mutually relatively rotate the fasteners.
In order to prevent such relative rotation of the fasteners, and thus unwinding of the spring element before the mandrel with it is inserted into the intended place, the forward fastener of the mandrel is conventionally arranged to be rigidly attached to a flexible shaft, and at the rear end of the probe to constrain the shaft and probe casing against relative rotation. Since the probe, comprising casing and shaft, must be flexible and can have considerable length, e.g. 60 cm, and often has a small outside diameter, e.g. 2 mm, the shaft and probe casing will have a considerable angle of mutual torsional twist. This twist comes partly from the torque elastically exercised by the helical spring element tightly wound up on the mandrel, and partly from the further torque which the operator applies to the probe casing and shaft for ensuring engagement of the spring element against the mandrel. This twist considerably increases the difficulty of checking and controlling the stress state of the spring element, paricularly since it is difficult to decide whether the twist comes from winding the element round the mandrel or from the probe casing and shaft.
One object of the invention is therefore to provide a device of the kind mentioned, which reduces or eliminates the mentioned drawbacks.
Further objects and advantages of the invention will be apparent from the following, or will be understood by one skilled in the art. The problem solved by the invention is particularly salient when it is desired to regulate the radial expansion of the spring element with regard to size and/or rapidity, since the relative rotation of the probe casing and shaft at the rear end of the probe will be information concerning the relative rotation of both fasteners, which is difficult to interpret.
A further object of the invention is to provide a device which, apart from affording a well-controllable expansion of the spring element, also allows winding the spring element about the mandrel at the place of implantation and/or permits positive expansion of the spring element at the implantation location, e.g. when the inherent ability of the spring element to expand radially and elastically is exhausted.